The overall objectives of our laboratory experiments are to establish an in vitro assay system for acute lymphoblastic leukemia of childhood. The goals for the current year were two fold: to perform experiments designed to optimize our in vitro system for growth of malignant lymphoid colony forming cells (ML-CFCs); and to establish dose response curves for the ML-CFCs to drugs in vitro. During the past year, we have focused on attempts to optimize the growth of our ML-CFCs. We have been able to enhance the cloning efficiency of most of our cell lines by 1 to 2 logs. This was obtained by optimizing media conditions and by modifying laboratory procedures so that the pH and temperature of our cells remained constant throughout the drug experiment. The pH was kept at 7.3 and the temperature at 37 degrees C while cells were at table top. Also, the benefits of supplemental zinc as well as calf serum, cord serum, and human serum were evaluated. Basically, specific cell lines showed enhanced growth when up to 40% serum was added. We have initiated studies on the effect of daily feeding on our colony forming cells and are beginning to look at the stimulatory effects of specific T-, B-, and null-cell line conditioned media. We have been able to establish in vitro sensitivity patterns of our cell lines on three vinca alkaloids (vincristine, vinblastine, and vindesine). Even though these vinca alkaloids are chemically very similar, different dose response curves resulted on the in vitro assay system. Granulocytic colonies were most sensitive to vinblastine (as would be expected) and the B-cell line was unusually sensitive to vinblastine. Clearly distinct dose response curves were obtained on multiple trials. An example of one study showed a B-cell line with the following results: drug dose that blocked colony formation by 50%, 1) vindesine, 0.1 ug/ml; 2) vincristine, 0.01 ug/ml; and 3) vinblastine, 0.001 ug/ml.